Dimitri was starting at Hogwarts, so the Burton family were going to Diagon Alley to get all of his school supplies, plus some things for Zhenya to take to Russia.
"First stop, Gringotts," said Alexander.
Zhenya was on his shoulders, and she was pulling out strands of his hair to play a game.

When they walked into Gringotts, Zhenya took a whole fist full of his hair, and Alexander screamed in pain. "OWW Zhenya," he said, pulling her gently off his shoulders. He put her on the ground and saw that she was frozen in fear. Approaching them... a Goblin.